Illumination System Correction for Lithography Image Size Variation
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Solution Overview
Problem
Optimization of illumination systems in projection exposure apparatuses for projection lithography often results in suboptimal imaging due to non-uniform intensity distributions across the object field, leading to variations in structure image size that are not adequately controlled, affecting the quality of micro- or nanostructured components.
Innovation Solution
A method and device for adjusting the illumination system by using a correction device, such as UNICOM, to optimize structure image size variation across the field height by differentially influencing individual imaging light partial beams, allowing for non-uniform intensity distributions that align with specific object structures, utilizing simulation or measurement to determine and adjust the intensity distributions and diaphragm positions for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the illumination system is adjusted to achieve uniform intensity distribution over the field height, then the illumination uniformity is improved, but the structure image size variation cannot be adequately controlled
Solution Approach 1:
The patent applies local quality by differentiating the adjustment approach for different regions of the field. Instead of uniformly adjusting all imaging light partial beams to achieve overall intensity uniformity, the method selectively adjusts individual partial beams based on their specific contribution to structure image size variation at different field positions. This allows non-uniform intensity distribution to be accepted in regions where it does not adversely affect imaging precision, while maintaining strict control in critical regions.
Solution Approach 2:
The patent changes the optimization parameter from intensity uniformity to structure image size variation control. By shifting the control target from a photometric parameter (intensity distribution) to an imaging quality parameter (structure image size), the system can accept non-uniform intensity distributions that do not degrade imaging precision, thereby resolving the contradiction between illumination uniformity and imaging quality.
2Illumination intensity
If the correction device adjusts all imaging light partial beams uniformly to achieve uniform intensity distribution, then the illumination uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent segments the illumination system into multiple independent imaging light partial beams, each with its own adjustable correction elements. This segmentation allows selective adjustment of only those partial beams that significantly contribute to structure image size variation, rather than uniformly adjusting all beams. The correction device is divided into multiple independently controllable units, reducing the overall complexity by enabling targeted adjustments.
Solution Approach 2:
The patent applies partial action by adjusting only the necessary subset of imaging light partial beams rather than all beams uniformly. By identifying and adjusting only those partial beams whose intensity variations significantly impact structure image size, the system achieves adequate imaging precision control with reduced adjustment complexity compared to comprehensive uniform adjustment of all beams.
3Illumination intensity
If the illumination system is optimized for uniform intensity distribution, then the illumination uniformity is improved, but the imaging result quality deteriorates
Solution Approach 1:
The patent inverts the traditional optimization approach by not seeking uniform intensity distribution as the primary goal. Instead, it accepts non-uniform intensity distribution and uses selective adjustment of imaging light partial beams to directly optimize structure image size variation. This inversion of the optimization target resolves the contradiction by making imaging result quality the primary objective rather than illumination uniformity.
Data Source
AI summary
A method includes moving a correction device into a neutral position; subsequently ascertaining, for a given arrangement of imaging light channels in the illumination optical unit of the projection exposure apparatus, intensity distributions of at least some of the individual imaging light partial beams along a transverse coordinate transverse to a displacement direction of an object to be imaged; subsequently ascertaining, in dependence on the transverse coordinate, an actual variation of actual values of structure image sizes of object structures in an image field, onto which the object is imaged; and subsequently specifying a predetermined variation of the structure image sizes over the transverse coordinate and displacing correction elements of the correction device, starting from the neutral position, such that the actual variation matches the predetermined variation within a tolerance bandwidth. The method can provide improved imaging results as compared to known uniformity adjustment.